"This ...is the Golden Snitch, and it's the most important ball of the lot. It's very hard to catch because it's so fast and difficult to see. It's the Seeker's job to catch it. You've got to weave in and out of the Chasers, Beaters, Bludgers, and Quaffle to get it before the other team's Seeker, because whichever Seeker catches the Snitch wins his team an extra hundred and fifty points, so they nearly always win. That's why Seekers get fouled so much. A game of Quidditch only ends when the Snitch is caught, so it can go on for ages--I think the record is three months, they had to keep bringing on substitutes so the players could get some sleep."
--Gryffindor Quidditch Captain Oliver Wood (PS10)

Commonly referred to as a Snitch, this is the smallest and fastest ball in the game of Quidditch.

Catching the Snitch originated in the 1100's from the Wizarding sport of chasing and catching a fast diminutive bird called a Golden Snidget (QA4).

Eventually Snidget numbers fell to a dangerously low level, and the Wizards' Council headed by Elfrida Clagg made them a protected species. As a substitute for the living bird, Bowman Wright of Godric's Hollow invented the Golden Snitch, a tiny metal ball with wings that zig-zagged and flew just like the original Snidget, but was more durable (obviously) and could be enchanted to stay within the boundaries of the Quidditch pitch (QA4).

A Snitch is never touched by human hands before a match, and the makers wear gloves. Only the Seeker is supposed to touch the Snitch (DH7).

In a Pensieve memory, Harry saw his father James releasing and catching a Golden Snitch, possibly trying to impress Lily Evans but mainly impressing Peter Pettigrew. James was a Chaser and not a Seeker, and when asked where he got the Snitch he said he "nicked it" (stole it) (OP28).

On his 17th birthday at the Burrow, Mrs. Weasley made Harry a cake shaped like a Golden Snitch (DH7). That same day he was told that Dumbledore's will had left him the first Golden Snitch he ever caught. Minister for Magic Rufus Scrimgeour told Harry it had a "flesh memory" as all Snitch's do, and would open only for him. Scrimgeour never knew, but inside the Snitch, Dumbledore had hidden the Resurrection Stone, one of the Deathly Hallows that came from Marvolo Gaunt's Peverell ring (DH22). The Snitch had the words "I open at the close" engraved upon it, and when Harry realised he had to sacrifice himself to Voldemort in order to save his friends he whispered "I am going to die" and the Snitch opened to reveal the Stone (DH34).

Commentary

Etymology

"snitch" = used elsewhere in the books to mean an "informer" or someone who betrays a trust, such as Marietta Edgecombe who told Umbridge about Dumbledore's Army and was stricken with pimples due to the "Snitch Jinx" from the enchanted parchment Hermione used for the D.A. List.

Notes

The Golden Snitches used as props for the movies were "electroformed in copper and then plated with gold" ( Harry Potter Page to Screen: The Complete Filmmaking Journey, via Pottermore).

Fan Theories:

In many ways, the Golden Snitch is a metaphor for Harry himself: the innocent young wizard who enjoyed flying and having fun became the "Chosen One" who was constantly sought out or chased (literally or figuratively) by everyone from the Daily Prophet to the Death Eaters, from the Ministry to Lord Voldemort. By the end of the story, the original Snitch from his first Quidditch match that brought him such joy became his way to cope with death, by resurrecting his family and friends who had already died to save him. Harry was just a pawn in a complex game started years before by Tom Riddle and Dumbledore, but just like the Golden Snitch, Harry was the only game piece which could bring the "match" to a close. As he says to himself while walking to his own death in the forest "The long game was ended, the Snitch had been caught, it was time to leave the air" (DH34).

Another theory is that the Snitch is a metaphor for Lily Evans and her love. Her future husband James said he "nicked" the Snitch he was playing with just before he attacked Severus Snape, a rival who also loved Lily. And because Snape was under so much distress from the attack, he slipped and called Lily a "Mudblood," the "unforgivable word" as Harry came to think of it (DH33). Yes, Snape had problems and Lily was fed up with him anyway, but James and the other Marauders bullied him on a regular basis to make him even less popular, and Sirius said that continued even after James said he had changed and began to date Lily (OP29). So Lily became the innocent pawn and the prize in the rivalry between the Marauders and Snape, not just a symbol of House rivalry, but also a sad commentary on House loyalty. For instance, even after Snape told Lily about the Werewolf prank that could have caused his death, she refused to believe that Lupin was a werewolf (DH33). By then, Sirius and James must have convinced her that Snape was crazy, or making up stories.